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| Subject: | Re: LF: Sound Card Impedance |
| From: | Stefan Schäfer <[email protected]> |
| Date: | Thu, 16 Dec 2010 14:46:22 +0100 |
| In-reply-to: | <[email protected]> |
| References: | <5BB571709EEB4C2084239E924B0EACEE@lindavideo> <[email protected]> |
| Reply-to: | [email protected] |
| Sender: | [email protected] |
| User-agent: | Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3 |
Johan, Am 16.12.2010 13:26, schrieb Johan H. Bodin: I measured the input impedance of the mic input on a Dell laptop: AC input impedance: 4.3 kOhms (-6dB with 4k3 resistor in series) Mic bias voltage: +3.8V (open circuit) Output current: 809uA (shorted to GND) This suggest that there is a 4k7 pull-up resistor to +3.8V for mic DC bias. It may vary somewhat between different brands and models of course but all soundcard mic inputs that I have seen so far puts out some DC bias for electret microphones. 73 Johan SM6LKM Interesting! Thank you for this information.Maybe one should think about this when designing a sensitive preamp output stage. I will keep it in mind. 73, Stefan/DK7FC |
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